1. Field of the Invention
This invention relates to a wafer prober, and more particularly to a wafer prober for inspecting electrical performance of a multiplicity of semiconductor element circuits formed on a semiconductor wafer.
2. Description of the Related Art
Semiconductor elements are produced so that a substantially disk-shaped thin sheet called a wafer is partitioned in a regular order longitudinally and latitudinally and a multiplicity of required electric element circuits identical with one another are formed in every partitions. Then, in the wafer formed thereon with the multiplicity of electric element circuits identical with one another, before cutting an element formed with an electric element circuit into a chips, the electric element circuits are inspected one after another by a semiconductor element inspecting device called a wafer prober, to thereby select and determine non-defective or defective. As shown in FIG. 3, this wafer prober 10 has a table 12. The table 12 is rested thereon with a wafer 14 and adapted to move horizontally in a direction X-Y and vertically in a direction Z in accordance with the arrangement of the plurality of electric element circuits formed on the wafer 14.
Furthermore, the wafer prober 10 is provided therein with a head stage 16 which is positioned upwardly from the table 12. The head stage 16 is secured thereto with a probe card 20 through a ring member 18. The probe card 20 is provided thereon with a plurality of probe needles 20A and 20B . . . , which are positioned at positions in association with respective electrodes of the electric element circuits to be inspected. As for this probe card 20, a probe card specialized for each type of the wafer 14 to be inspected should be prepared, and, in the specialized probe card, it is clearly indicated the type, mark and the like regarding the wafer 14 to be inspected. Accordingly, whenever the type of the wafer 14 to be inspected in changed, a specialized probe card should be secured to the ring member 18.
Further, the head stage 16 is provided with a test head 22 which is fixed thereto with an arm 24. The arm 24 is rotatably supported by a main body 28 of device through a shaft 26. A plurality of base plates are received in the test head 22. The plurality of base plates are electrically connected to a tester through a cable. These plurality of base plates are electrically connected to a performance board, not shown, which is detachably secured to the test head 22 through a holding frame 32. (Incidentally, the performance board can be detachably secured to the ring member 18).
Then, when the test head 22 is positioned at an inspecting position, the performance board is electrically connected to the probe card 20 through the ring member 18. With this arrangement, the tester is electrically connected to the probe card 20, and, when the probe needles 20A and 20B . . . are connected to the electrodes of the respective electric element circuits of the wafer 14, the tester inspects the respective electric element circuits.
Now, the shaft 26 is fixed thereto with a link 40, and a rod 42A of an air cylinder 42 is rotatably supported by the end portion of the link 40. Furthermore, a cylinder portion of the air cylinder 42 is rotatably supported by a main body 46 of device. Then, when the air is supplied to the air cylinder 42, the balancing force is rendered to the link 40, whereby the weight of the test head 22 is offset.
The balancing force of the air cylinder 42 will hereunder be described. In the relationship shown in FIG. 4, as viewed from the balancing between the moments, the following equation (1) will be established ##EQU1##
where
R:the balancing force of the cylinder 42 PA1 D:the distance from the center of the shaft 26 to the position of the center of gravity of the test head 22 PA1 W:the weight of the test head 22 PA1 d:the length of the link 40 PA1 .theta.:the angle of rotation of the test head 22 PA1 .alpha.:the angle between the balancing force R of the cylinder 42 and the tangent line PA1 L:the distance between the pin 44 and the shaft 26 PA1 M:the length of the cylinder 42
Furthermore, from the relationship of a triangle S consisting of O.sub.1, O.sub.2 and O.sub.3 as shown in FIG. 4, the following equation (2) will be sought. ##EQU2##
where
The following equation (3) will be sought from the equations (1) and (2). ##EQU3##
Further, from the relationship of the triangles S consisting of O.sub.1, O.sub.2 and O.sub.3 as shown in FIG. 4, the following equation (4) will be sought. EQU M.sup.2 =L.sup.2 +d.sup.2 -2dLcos (90-.theta.) (4)
From the equations (4) and (3), the following equation (5) indicating the balance force R of the air cylinder 42 will be sought. ##EQU4##
As shown in the equation (5), since the balancing force R of the cylinder 42 is represented by a function, the balancing force R of the cylinder 42 is fluctuated in association with the rotation angle .theta. of the test head 22.
When the balancing force R of the air cylinder 42 is fluctuated in association with the rotation angle .theta. of the test head 22 as described above, then, if a worker rotates the test head 22 upwardly, then the worker cannot rotate the test head 22 by an operating force of a predetermined value, whereby such a problem has been presented that the operation is difficult to do.
Furthermore, when the rotation angle .theta. of the test head 22 is changed, there is some angle at which the weight of the test head 22 cannot be offset by the balancing force of the air cylinder 42, so that such a problem has been presented that, in the case of this angle, the test head 22 cannot be balanced by the air cylinder 42.
To eliminate this problem, there is disclosed a device for maintaining the balancing force of the cylinder at a predetermined value without being influenced by the rotation angle of the test head (Japanese Patent Application Laid-open No.2-74050). However, this device of this Patent Application Laid-open has been constructed in such a way that the cylinder for balancing is moved by another cylinder in order to maintain the balancing force of the cylinder, so that such a problem has been presented that the construction becomes complicated.